Well you should atleast state the issue. are you getting network busy or any other rejection. based on rejection the issue can be multiple. in our network the issue was that once a number seriese of Landline was not defined which resulted in calls not being made to that no seriese.
If the issue is of Mute calls check the interconnect E1s for issues.
If there is network busy check if the Aters interconnecting don’t get congested.